The present invention relates to an apparatus and method for alarming decrease in tire air-pressure. More particularly, the present invention relates to an apparatus and method for alarming decrease in tire air-pressure capable of properly informing a decompressed condition of a tire to a driver of a vehicle such that the driver can drive safely.
It is conventionally known for a system for alarming decrease in tire air-pressure (DWS) for detecting decompression of a tire based on rotational (wheel speed) information of four wheels. Such a system is based on the theory that a rotational velocity or rotational angular velocity of a decompressed tire is increased when compared to that of other normal tires since its outer diameter (dynamic load radius of the tire) is. decreased in contrast to tires of normal internal pressure. In a method for detecting decrease in internal pressure on the basis of a relative difference of rotational angular velocities of tires (refer to Japanese Unexamined Patent Publication No. 305011/1988), a judged value DEL is defined as follows:
DEL={(F1+F4)/2xe2x88x92(F2+F3)/2}/{(F1+F2+F3+F4)/4}xc3x97100(%)
In case the judged value exceeds a threshold which has preliminarily been properly adjusted, the driver is informed of a decrease in internal pressure. Here, F1 to F4 indicate rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively. In such a method, in case the threshold is so adjusted that decompression of a tire by 30% from a normal internal pressure is surely detected, the driver is alarmed of decompression in case the internal pressure has decreased by approximately 30%.
In case adjustments are performed to detect decompression of the internal pressure of a tire by 30% in the conventional method, no information is supplied to the driver until decompression has progressed to 30%. That is, no information is given until the set threshold has been exceeded. If the driver would be informed of a decompressed condition in which the decompression gradually progresses or decompression has progressed to 20%, it can be prevented that a sudden alarm causes anxieties to the driver but the driver could perform safe driving and could accordingly arrange for repair of the tire in question.
The present invention has been made in view of the above circumstances, and it is an object thereof to provide an apparatus and method for alarming decrease in tire air-pressure capable of properly informing a decompressed condition of a tire to a driver of a vehicle such that the driver might drive safely.
In accordance with the present invention, there is provided an apparatus for alarming decrease in tire air-pressure for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a vehicle, comprising: a. rotational information detecting means for detecting rotational information of the respective tires; a rotational information memory means for storing the rotational information of the respective tires; a judged value calculating means for calculating judged values based on the rotational information of the respective tires; a judged value memory means for storing the judged values; a transition calculating means for calculating transition of the judged values based on the stored judged values; a judging means for determining a decrease in tire air-pressure based on the judged values; and an alarming means for issuing preliminary alarm prior to issuing a predetermined alarm for informing decrease in internal pressure based on the transition of the judged values in case the judged value tends to move to exceed a predetermined threshold for determining a decrease in internal pressure.
In accordance with the present invention, there is further provided a method for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a vehicle, comprising the steps of: detecting rotational information of the respective tires; storing the rotational information of the respective tires; calculating judged values based on the rotational information of the respective tires; storing the judged values; calculating transition of the judged values based on the stored judged values; determining a decrease in tire air-pressure based on the judged values; and issuing preliminary alarm prior to issuing a predetermined alarm for informing decrease in internal pressure based on the transition of the judged values in case the judged value tends to move to exceed a predetermined threshold for determining a decrease in internal pressure.